Hair extension



FIG. 1 is a perspective view of a hair extension showing my new design.

FIG. 2 is a front view thereof.

FIG. 3 is a back view thereof.

FIG. 4 is a right side view thereof.

FIG. 5 is a left side view thereof.

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines shown in the drawings depict portions of the hair extension that form no part of the claimed design. 

CLAIM The ornamental design for a hair extension, as shown and described. 